1. Field of the Invention
The present invention relates to a method for producing a conductive oxide pattern which can be used in a liquid crystal display or an image sensor or the like.
2. Description of the Prior Art
In recent years, a large-size liquid crystal display and image sensor having a substrate and a conductive oxide pattern on the substrate have become more common. Hand in hand with this trend, the substrate having the conductive oxide pattern have also increased in size. This has led to a high degree of technological innovation in the fabrication of this type of large-area substrate with good efficiency and at low cost.
In a conventional technology for a manufacture of the substrate having the conductive oxide pattern, for example in the case of ITO(indium tin oxide) film, the ITO film is formed on an insulating substrate by commonly known vaporization or sputtering methods. At this time, the substrate is heated to 250.degree. to 400.degree. C. and oxygen is introduced to lower the resistivity and increase the translucent characteristics of the ITO. As the area of the ITO is increased, a further decrease in the resistivity value is required and the temperature at which the ITO film is formed is generally increased. Following this formation of the ITO film, a resist is formed in the specific pattern on the ITO film, using commonly known photolithography technology. Next, etching is performed, using the resist as a mask. For wet etching, etchants such as hydrochloric acid+ferric chloride, hot hydrochloric acid+ferric chloride, are used where zinc powder can be used in place of the ferric chloride. The ITO film is etched by the etchants to render a portion of the ITO film under the resist remain and the substrate having the remaining portion of the ITO film is used in liquid crystal displays, image sensors, and solar cells, and the like. Dry etching is not frequently used because no activated type of etchant has been found which provides a conductive oxide pattern of ITO or the like with good etching efficiency. Also, because the etching rate is low, the dry etching is not suitable and not practically used for processing a large area substrate of liquid crystal displays, solar cells, and the like.
The following problem areas are inherent in these methods. The tact time of the manufacturing process of the ITO film is long. Specifically, after the substrate is set in a vacuum device to form the ITO film, the substrate is heated to a predetermined temperature so a waiting period is necessary. If the temperature of the substrate is suddenly lowered to room temperature after the film has been formed, the formed ITO film tends to peel from the substrate. Therefore the temperature must be reduced gradually. As a result, one batch of ITO film takes a relatively long time to produce. Because the process requires heating in a vacuum, it is difficult to obtain a uniform temperature distribution, therefore it is necessary that a heating device is provided more extensively than the ITO film is formed on the substrate. This increases the size of a reaction chamber. In addition, the reproducibility is poor because of the heating process. An ITO film which is formed with the substrate heated in this manner is extremely dense and has an extremely low electrical resistance. Accordingly, a powerful etchant is required to etch this ITO film in a predetermined pattern. In addition it is necessary to heat the etchant during the etching process in order to increase the etching rate.
When the ITO film is etched with a powerful etchant of this type, the edge of the etching pattern loses its sharpness and the pattern undulates. Also, a large volume of hydrogen is produced which causes the etching pattern mask to peel away or sustain damage during etching. It is therefore extremely difficult to obtain a fine etching pattern on a large-area substrate.